1. Field of Endeavor
The present invention relates to the field of electric heavy-duty generators, and more specifically to an inspection vehicle for inspecting an air gap between the rotor and the stator of such a generator.
2. Brief Description of the Related Art
The inspection of air gaps in large generators in the assembled state has the advantage that the rotor does not have to be withdrawn from the generator, but only minimal operations need to be undertaken for opening the casing. This leads to great time savings and shortens the downtimes of the generator considerably.
For the inspection, an inspection device is introduced into the air gap, that is to say into the gap between rotor and stator, with which the outer surface of the rotor can be inspected visually and electromagnetically, as well as the inner surface of the stator. Furthermore, the mechanical integrity of the windings and the associated winding wedges can be checked. The air gap customarily has a width of between 10 and 30 mm, but with the rotor installed, the width of the access between the end ring of the generator and the stator may even be only about 9 mm.
In the past, a large number of devices for in-situ inspection in the air gap of generators have already been proposed. All known devices and methods have some disadvantages. Often, they are not universal enough to be easily adapted to the different generator geometries, and the devices are frequently too large to be introduced through a standard inspection opening in the generator. Their size leads to a partial opening of the casing, which costs valuable time and leads to an outage of the machine.
In the prior art, three main families of in-situ inspection devices for the air gaps of generators can be distinguished: the first can be referred to as a “cable car” device. Such a device is schematically shown in FIG. 1. A sensor carrier 15 is introduced into the air gap 14 of the generator 10 between a central rotor 11 and a stator 12 which concentrically encloses the rotor 11, and is fastened on a wire 18 which is guided in the axial direction through the air gap 14 and by reels 16 and 17, which are arranged at the ends, can be moved back and forth in the axial direction (see the double arrow). A comparable device is disclosed in printed publication EP 1 233 278 A2. In the case of this device, it is disadvantageous that, with simultaneous removal of large parts of the casing, the device has to be inconveniently fastened on the generator.
A second family, the construction of which is schematically reproduced in FIG. 2, instead of the continuous wire uses a thin, inherently stiff band 19, on the free end of which the sensor carrier 15 is fastened. The band 19 can be displaced in the axial direction by a roll-up mechanism 20. As in the case of the solution of FIG. 1, in this case the roll-up mechanism can be moved around the rotor 11 in the circumferential direction in order to reach all regions of the rotor top surface or of the stator inner surface with the sensor carrier 15. Also in this case, the main disadvantage lies in the fastening on the generator and the disassembly cost which is associated therewith.
The third family of inspection devices, which is schematically shown in FIG. 3, includes a robot 21 as the central component, which can be moved autonomously in the air gap 14 by it being rolled over, and consequently moved along, the surfaces of the rotor 11 and of the stator 12 via tracked drives 22, 23 which are arranged on the upper side and lower side. The tracked drives 22, 23 are pressed onto the respective surface by a spreader mechanism in the process in order to achieve sufficient friction for the drive and accurate positioning. Such a solution is known for example from printed publication US 2008/0087112 A1. Such a robot on the one hand is very costly in construction and operation, and on the other hand is not compact enough to be introduced from the outside into the air gap of different generators and to be moved in all regions there.